A recent development in our country has been the rapid growth of the utilization of controlled access information--more especially cable and satellite scrambling television. Typically the controlled access information is transmitted in a scrambled form with the access thereto dependent upon the unscrambling of the signal at the point of reception. Currently this unscrambling occurs in an expensive digitally controlled decoder such as the M/A-Com Video Cipher II or the familiar cable black box. There is, needless to say, considerable consumer resistance to the cost of decoding the scrambled signals. However with the need to constantly vary the scrambling of the signals to avoid privateers a decoding system less expensive would not suffice: If a scrambling system is easy to break it will be.
The present invention is directed at a way of reducing the cost of transmission of the scrambled signals while increasing the security of the overall distribution network.